T. r. devices



Oct. 16, 1962 W, 1 SCOTT ErAL 3,059,193

T.R. DEVICES Filed March 24. 1959 g77-ORNE rf www United States Patent"ice 3,059,193 T.R. DEVICES William Joseph Scott and Francis LucasCrowther, Rugby, England, assignors to Associated Electrical Industries(Rugby) Limited, London, England, a British company Filed Mar. 24, 1959,Ser. No. 801,477 Claims priority, application Great Britain Mar. 31,1958 3 Claims. (Cl. 33313) This invention relates to T.R. devices of thekind used in connection with radar equipments utilising a common aerialsystem for transmission and reception for protecting the receiver of theequipment from the energy supplied to the aerial for the transmitter. Transmit-receive (TR.) cells, transmitter-blocker (TB.) cells and pre-T.R. cells are examples of such devices and will be collectivelyreferred to hereinafter under the term TR. de-

vices.

T.R. devices of the kind to which the invention relates employ aresonant slot tuned to the frequency of the oscillations to betransmitted and received which is enclosed within an evacuated spacecontaining, usually an inert gas such as argon plus some water-vapour. Acommon construction is to provide the slot in a metal diaphragm arrangedtransversely across a wave guide through which the oscillations aretransmitted, the slot being iilled with glass hermetically sealed to themetallic rim of the slot so as to form a resonant window, the diaphragmsealing off a section of the wave guide which is evacuated and filledwith inert gas and water vapour as above stated or other arc quenchingagent. When oscillations of high energy pass through the section of waveguide, an electric discharge occurs across the slot. If the energy sodissipated is not unduly high, no adverse eects are experienced; but ifthe energy dissipated is raised to a high value, the intense ionisationand products produced by the arc have been found to render the deviceunusuable after a comparatively short space of working life.

The c'oject of the invention is to improve the operation of 'IIR'.Vdevices of the kind above described by increasing their life.

A further object of the present invention is to prevent the 'productsproduced by the discharge across the slot from interacting with themetal in the vicinity of the slot and elsewhere in diffusing distance.

According to the invention an enclosure for the window constituting theresonant slot of a T.R. device is provided -in the form of a member ofvitreous material having a hollow in one face thereof, said member being1ocated with the hollow facing the window and in proximity thereto sothat the atmosphere within the device can enter the hollow and so thatthe inside of the enclosure is of glass or other vitreous material. Theenclosure thus prevents the intense ionisation produced by the dischargefrom reaching the Wall of the T.R. device and producing undesired arcingproducts.

The member may be in the form of a block of vitreous material having aconcavity in one face thereof; a1ter natively the member may be in theform of a hollow box built up from parts of vitreous material.

The member may be retained in proximity to the window by means ofprojections from the internal wall of the TR. device, against which themember abuts when the member is introduced into the device prior to theaflixing of the frame containing the resonant slot as an end closuremember of the device.

The projections may be made by nicking the inner wall of the device witha sharp instrument so as to produce burrs, or by narrow ledges brazed tothe walls. In T.R. cells in which the resonant slot is provided in atransverse wall across a section of waveguide of rectangular cross-3,059,193 Patented Oct. 16, 1962 section, a wide inductive iris spacedfrom the transverse wall may be arranged to support the block.

The invention will be better understood on consideration of thefollowing description of the accompanying drawings, in which:

FIG. 1 shows in elevation and partly in cross section a T.R. cell of thekind embodied in a section of wave guide of rectangular cross section.

FIG. 2 is a cross section of FIG. 1 on the line II-II of FIG. 1,

FIG. 3 is a perspective view of the vitreous block shaped to form aprotection for the resonant slot in the TZR. de-

vice,

FIG. 4 is an elevation partly in cross section of an alternative form ofT.R. device embodying the invention, and

FIG. 5 is a cross section of a part of the TR. device shown in FIG. 4 onthe line V-V of yFIG. 4.

The form of T.R. device illustrated in FIGS. 1 and 2 consists of a shortsection `1 of waveguide of rectangular cross section terminated by anges2 through which it can be connected to adjacent sections of waveguide.The section is sealed at its ends by transverse metal walls 3 eachcontaining a window constituting a resonant slot 4, the longitudinalaxis of which is parallel to the wider dimension of the waveguidesection. The resonant slots are sealed by glass 5 hermetically sealed tothe wall 3 at the rim of the opening therein and covering the near faceof the adjacent wall around the slot, as is clearly shown in FIG. 1.Spaced from the wall 3 is formed an opening 6 or inductive iris limitedby transverse walls 7 which extend inwardly from the narrow walls of thewaveguide and by narrow projections 8 extending inwardly from the widerwalls of the guide. Conical electrodes 9 between which a gap is presentare provided in a manner customary with T.R. devices of the characterillustrated, across which a discharge takes place when high frequencypower greater than a predetermined value passes through the TR. device.

In order to protect the window formed by the resonant slot 4 and thesurrounding wall of the T.R. device from the effect of intenseionisation produced when oscillations of high energy pass through thesection by the waveguide, there is provided in the neighbourhood of theslot an enclosure consisting of a block d0 or box d0 of vitreousmaterial or of more than one vitreous material having a hollow in theform of a concavity |11 in one face thereof, the block being locatedwith the concavity facing the window and in proximity thereto asillustrated. The block 10 is not integral with the glass 5 hermeticallysealed in the window so that the atmosphere within the device can enterthe concavity, the interior wall of the enclosure formed thereby beingthus of glass or vitreous material which is inappreciably affected bythe discharge across the window. The block 10 which is shown inperspective in IFIG. 3 is preferably of fused silica and of rectangularform, Where the waveguide section i1 is rectangular in cross section.The concavity \11 in the block may conveniently be in the form of ashallow depression of cylindrical contour bounded by side walls 12 whichare substantially vertical to the planes containing the faces 13 of theblock, the side walls -12 lying parallel to the wide dimension of theWindow. The depression 11 may be produced by grinding one face of arectangular plate of fused quartz with a grinding or lapping wheel. Theplate may have, for a T.R. device suitable for centimetric waves of 3.2cm. wavelength, a length of the order of 0.9", a Width of the order of0.4 and a thickness of the order of 0.125, the depression reducing thethickness at the centre of the block to about 0.024". The depression isso located as to leave a plane rim around it having a width of about0.032.

In the arrangement shown in FIGS. 1 and 2, the block ishheld iirmly inposition in proximity to the window by the wall 1 and the resilientpartitions 8 forming the iris 6. The electrical function of the iris 6is to tune out the capacity introduced by the shield formed by the block10. The T.R. device is normally lled with a mixture of rare gas andwater vapour, in which the discharge across the resonant slot takesplace, for example, a lling of krypton at a pressure of l millimetres ofmercury, and water vapour at a pressure of 4.5 millimetres of mercurymay be employed.

In the arrangement shown in FIGS. 4 and 5, a different form of T.R.device is illustrated, the device consisting of a T.B. cell utilisingthe protective window of the invention. 'I'he cell consists of a section14 of rectangular waveguide closed at one end by the transverse metalwall :1S containing the sealed resonant aperture or window 4 inproximity to which the block =10 is located. The far end of the sectionof waveguide is completed by a mounting flange 16 through which passesan evacuating tubulation 17. In this construction means for tuning thewindow to resonance at a predetermined frequency is illustrated,consisting of a iiexible metallic diaphragm 118 which is -placed overthe window and is secured to the broad walls of the wavegulide section14, e.g. by brazing. The diaphragm :18 is provided with a tuning bar y19secured thereto, the tuning bar having a screw-threaded bore -20 bymeans ofwhich its position with relation to the window can be adjustedby means of a screw-threaded rod Vintroduced temporarily into theinterior of the section y14 through the evacuating tubulation -17 beforethe latter is sealed oi. The diaphragm 18 provides for the adjustment ofthe resonance frequency of the cavity between the diaphragm 18 and thewindow 4, including that necessitated by any departure from apredetermined value by the presence of the di-electric body 10introduced into the cavity.

FIGS. 4 and 5 also illustrate an alternative way by which the block 10may be secured into position, the edges 21 of the diaphragm 18 below thepoint at which the diaphragm is secured to the wall of the waveguidebeing turned inwards to prevent the block 10 from becoming displacedfrom its position adjacent the window 4. Preferably a separate springshim of metal (not shown) is placed between the side of the arc shield10 and the waveguide to hold the shield rmly in position. Otherarrangements for retaining the shield in position may, however, beadopted.

In an alternative arrangement the block may be held in position bynicking the inner wall of the waveguide 14 with a sharp instrument toproduce burrs against which the rear of the block may be retained. Theblock is inserted into position against the burrs prior to the end wall15 containing the resonant slot, being secured, e.g. by soldering, tothe wall of the waveguide section.

A batch of nine TB cells made as shown in FIG. 4, was put on life testat 200 kw. pulse power. All nine cells were satisfactory at over 1,600hours; a result much superior to that obtained with cells without arcshields.

Although the block 10 has been illustrated as being of rectangularshape, any other suitable shape may be employed provided the concavty inthe block is suicient Vsubstantially to enclose the window across whichthe discharge is to take place. Instead of making the block 10 from onepiece of vitreous material, it may be built up in the form of a hollowopen-sided box from sheets of vitreous material. For example, ceramicsheet glazed on one face, may be cut into pieces to form the sides andend of a box, the pieces being secured together, after assembly, byheating in a furnace, the glaze melting and subsequently solidifying tosecure the pieces together at their edges. It is also permissible forthe face of the block or box in which the hollow or concavty 11 ispresent to be non-planar, if desired.

What we claim is:

' 1. A T.R. device comprising a section of waveguide, transverse metalwalls sealing the ends of said section, at least one of said wallshaving a window in the form of a resonant slot sealed by glasshermetically fused to the edges of said slot and covering the inner faceof said Vone wall, said section having been evacuated and containing alling of an inert gas and water vapour, a rectangular hollow block ofvitreous material located Within said section and being of such size asto allow a space between the inner wall of said waveguide and the outerside walls of said block, said-hollow block hav-ing an open face on theside thereof arranged adjacent to said window and presenting a concavtytoward said window in which concavity said lling is present, and meansextending from the walls of said section for retaining said hollow blockin proximity to said window spaced from said window transverse wallwhich cooperating with said` spacing from the inner walls of saidwaveguide provides a space around said hollow block through which acontinuing supply of said filling enters said concavty.

2. A T.R. device according to claim 1, in which the hollow in said blockis in the form of a depression of cylindrical contour bounded by sidewalls substantially perpendicular to a plane containing said open faceof said block.

3. A T.R. device comprising a section of rectangular waveguide,transverse metal walls sealing the ends of said section, at least one ofsaid Walls having a window in the form of a resonant slot sealed byglass hermetically fused to the edges of said slot and covering theinner face of said one wall, said section having been evacuated andcontaining a filling of an inert gas and water vapour. a rectangularhollow block of lvitreous material located-.within said Vsection andbeing of such a size as to allow a space between the inner wall of saidwaveguide and the outer side walls of said block, said hollow blockhaving an open face on the side thereof arranged adjacent to said win,-dow and presenting a concavty toward said window in which concavty saidfilling ,is present, a wide inductive iris spaced from said transversewall containing said resonant slot, said iris being secured to the wallof said section and retaining said vitreous member in proximity to saidwindow spaced from said window transverse wall and from said iris sothat a continuing supply of said filling enters said concavty.

References Cited in the tile of this patent UNITED STATES rPATENTS2,791,720 Lesch May 7, 1957 2,929,035 Winslow et al Mar. 15, 19602,939,044 Stanney et al May 31, 1960 2,972,083 Walker et al Feb. 14,1961

